following a drought on Daphne Major, the beaks of the offspring of the surviving medium ground finches (average 14mm) were larger than the beaks of the entire population prior to the drought ( 12mm average). Based on the prior study, it is known that the heritability of beak size in the parental population was .5

what is true:
a. the selection differential was 4 mm
b. the ofspring are more variable than the parents
c.small beaked finches died in order to ensure the species' survival
d. the big beak offspring are a new species different from their medium beak parents